The data communications industry has established the fiber distributed data interface (FDDI) as a standard for the definition of the properties of a local area network. A system in accordance with that standard is referred to as an FDDI system and is an optical system port to port operating at a data line rate of 125 megabits per second.
FDDI is the first, all optical fiber high speed local area network system and will become prominent in the last decade of the twentieth century. It will provide a high speed optical transmission path between mainframe and peripheral equipment and is suitable for use as a backbone network between lower speed local area networks. FDDI presently is a 100 megabit LAN transfer data rate system that recommends a 62.5/125 micron core/cladding diameter optical fiber and is an LED based standard involving dual, counter-rotating, token passing rings that operate at a center wavelength of 1300 nm.
Dual rings include a primary ring and a secondary ring. Dual rings are used to provide enhanced reliability and an option for higher performance. If both rings are operative, the capability of transmitting in both ring directions exists.
The large scale use of optical fiber for the local area network will result in an extensive use of optical fiber in building distribution systems. The FDDI system presents several challenges. There are restrictions imposed by FDDI standards and there are complications associated with large quantities of fiber that include fiber which extends to individual work stations.
In order to aide network engineers and installers in enforcing basic rules and/or more restrictive policies which may be chosen by the user, the FDDI standard has defined certain requirements. For example, details of a receptacle for a dual fiber connector are specified in a standard referred to as the Physical Layer Medium Dependent (PMD) part of the FDDI standard. The PMD determines the specifications for optical transmitters and receivers, optical fiber, optical connections and optical bypass switches along with optional keying configurations. The receptacle and an associated plug are polarized mechanically to prevent the transposition of transmit/receive fibers, and keys corresponding to station interfaces are designed to avoid mixing primary and secondary rings and to avoid mixing station attachments. Viewing a station with the key on top, the transmit signal always exits the interface on a left fiber port, and the receive signal always enters the interface on a right fiber port.
A simple dual ring architecture can be arranged with the keying and signal directions defined in the PMD standard by using duplex jumper cables. The primary ring is constructed by connecting a B receptacle of each station to an A receptacle of the next station in a forward direction around the primary ring. When the primary ring is closed, the secondary ring is completed with the secondary ring signal flowing in an opposite direction.
As the network expands to multiple floors of a single building or to a campus including multiple buildings, connections become prohibitively complex to administer. For such expanded networks, it should be clear that a manageable distribution system is necessary. A sought-after system which includes simplistic rules for installation and administration of jumper cables is disclosed in application Ser. No. 401,354 which was filed on Aug. 31, 1989 in the names of R. M. Kimball and T. McIntosh.
Connectors must be provided to terminate jumper cables each of which includes two optical fibers. It is these jumper cables which are used in administrative locations such as in an equipment room and in riser and satellite closets to make cross-connections between interfaces in which cable runs terminate. The connectors are duplex connectors each being capable of terminating two optical fibers.
The FDDI connector typically comprises two plugs or ferrules, as they usually are called, each of which terminates an optical fiber. The two ferrules are mounted in a housing which has an entry end for a duplex cable. Each of the ferrules is spring-loaded to allow the connection between two ferrules to be loaded.
Duplex connectors for optical fiber are known in the art. For example, see U.S. Pat. No. 4,787,706 which issued on Nov. 29, 1988 in the names of T. C. Cannon, Jr., A. W. Carlisle and B. V. Darden. That connector includes a housing in which are mounted two ferrules. Each of the ferrules which terminates an optical fiber extends from an end of the housing opposite to that end into which a cable enters. The protruding ends of the ferrules are protected by a retractable bumper or shroud which may be moved rearwardly toward the opposite end of the housing to expose the ferrule ends and facilitate optical connections to other ferrules. Although the connector which is disclosed in the above-identified T. C. Cannon, et al. patent is suitable for duplex connections, FDDI standards are such that any shroud which covers the exposed ends of the ferrules invariably must be fixed in position.
The ferrules in such a connector have a propensity for becoming contaminated with dust, for example. Such contamination can affect adversely the performance characteristics across the connection. Accordingly, it is desired to be able to access the ferrules so that they may be cleaned from time to time.
Also of interest in the FDDI system is the ability to key different connectors for purposes of installation and administration. This has been accomplished with an arrangement such as, for example, that in the duplex connector disclosed in the above-identified Cannon et al. patent.
What is needed and what seemingly is not disclosed in the art is a connector for use with the FDDI which is relatively easy to manufacture. The sought-after connector should have provisions for protecting extending end portions of fiber terminating ferrules as well as allowing the end portions of the ferrules to be cleaned. Further, it is desired that the sought-after connector include keying provisions to simplify installation and administration of the connector in a network system.